Fano Resonance Research Articles

Four-state Fano resonance electro-optical modulator and sensor based on double borophene-dielectric grating structure

In this paper, we propose a borophene-based double-dielectric-grating structure (BDDGS) to realize the Fano resonance electro-optical modulator and sensor. The Fano resonance originated from the coupling of two resonance modes excited by the upper borophene grating (UBG) and the lower borophene grating (LBG). The coupling mode theory (CMT) is utilized to fit the Fano transmission spectrum. The calculated result fits well with the simulated spectrum. We found the Fano resonance wavelengths exhibit a blue shift with increasing the carrier density of the borophene layer. Further, we utilize this property to achieve a Four-state Fano resonance electro-optical modulator. The working wavelengths of the ON-ON (11), ON–OFF (10), OFF–ON (01), and OFF-OFF (00) states are 1.321 μm and 1.676 μm, respectively. The asymmetric Fano spectra exhibit high sensing sensitivity S=21THz/RIU and figure of merit FOM=3.9RIU−1. Moreover, our proposed structure possesses a slow-fast light effect with the maximum group index are 57.84 and −332.3, respectively. Although several Fano resonance and electro-optical modulators based on two- dimensional (2D) material, like graphene, black phosphorus, and transition metal dichalcogenides (TMDs) are previously reported, this paper designed a borophene-based metamaterial to achieve Fano resonance electro-optical modulator and sensor, because borophene possesses a series of excellent physical and chemical properties, for example, mechanical compliance, high carrier mobility, and optical transparency. Therefore, the proposed borophene-based metamaterial will be beneficial in the fields of high-performance plasmonic sensors, slow light, and electro-optical modulators in the near future.

Highly Sensitive Plasmon Refractive Index Sensor Based on MIM Waveguide.

This paper introduces a novel plasmon refractive index nanosensor structure based on Fano resonance. The structure comprises a metal-insulator-metal (MIM) waveguide with an inverted rectangular cavity and a circle minus a small internal circle plus a rectangular cavity (CMSICPRC). This study employs the finite element method (FEM) to analyze the sensing characteristics of the structure. The results demonstrate that the geometrical parameters of specific structures exert a considerable influence on the sensing characteristics. Simulated experimental data show that the maximum sensitivity of this structure is 3240 nm/RIU, with a figure of merit (FOM) of 52.25. Additionally, the sensor can be used in biology, for example, to detect the concentration of hemoglobin in blood. The sensitivity of the sensor in this application, according to our calculations, can be 0.82 nm∙g/L.

Multi-Fano resonances by TCS and resonance-enhanced TES in hybrid photonic crystals for ultracompact sensing

This work introduces a novel hybrid photonic crystal (PC) architecture exploiting topologically multi-Fano resonances employing an inverted π-shape structure filled with a nontrivial PC flanked by M−shaped trivial PCs for ultracompact and high-sensitivity sensing, harnessing their immense potential for miniaturized sensing applications. Topological corner state (TCS) is formed in the structure. Moreover, a waveguide-branch resonator or a resonant ring for the topological edge state (TES) mode is formed to increase the Fano resonance. We demonstrate the existence of engineered quasi-bound multi-Fano resonances within this structure, exhibiting tunable quality factors exceeding 108 (ultrahigh Q) and a remarkable figure of merit (FOM), reaching 2.6×107RIU-1. By precisely controlling the nontrivial PC dimensions, we achieve exquisite control over the resonance’s Q factor and spectral line shape, revealing characteristics of quasi-bound states in the continuum (BICs). This hybrid architecture exhibits exceptional sensitivity to refractive index changes, with tunability ranging from 320 to 392 nm/RIU. Our work paves the way for a new paradigm in sensing, enabling the development of ultracompact on-chip nanophotonic devices with unprecedented sensitivity and control.

Double-parameter analysis of an asymmetric herringbone temperature and refractive index sensor based on all-dielectric metasurface

The all-dielectric metasurface is a tremendously efficacious path to seek out planar optical manipulators. The application of extremely sensitive optical sensors is expected to benefit from the Fano resonances created in all-dielectric metasurface. An optical sensor basaed on the all-dielectric hollow herringbone metasurface is tuned for high-sensitivity temperature sensing and refractive index sensing. In the continuous near-infrared band, two resonance responses activated by magnetic toroidal dipole and magnetic quadrupole can be generated simultaneously. According to the simulation results, a superior properties refractive index sensor holding a Q factor as high as 2.6 × 104 is achieved, its maximum FOM of 3980 RIU−1 is displayed, and its sensitivity is 232 nm/RIU. And sensitivity of the temperature sensor is proved to be 63 pm/K, which shows a prominent improvement in temperature sensing. After analyzing it in the experiment, it is found that the Q factor is 5366 and FOM of 465 RIU−1, with the sensitivity of 178 nm/RIU. This refractive sensor provides a favorable groundwork for developing high-sensitivity sensing devices in many biochemical disciplines, which also increases the extensive application possibilities for biochemical analysis and environmental detection.

Optical switching with high-Q Fano resonance of all-dielectric metasurface governed by bound states in the continuum

The discovery of bound states in the continuum (BIC) of optical nanostructures has garnered significant research interest and found widespread application in the field of optics, leading to an attractive approach to achieve high-Q (Quality factor) Fano resonance. Herein, an all-dielectric metasurface consisting of four gallium phosphide (Gap) cylinders on the MgF2 substrate is designed and analyzed by the finite element method (FEM). By breaking the symmetry of the plane, specifically by moving the two cylinders to one side, it is possible to achieve a transition from the symmetry-protected BIC to quasi-BIC. This transition enables the excitation of sharp dual-band Fano resonance at wavelengths of 1,045.4 nm and 1,139.6 nm, with the maximum Q factors reaching 1.47 × 104 and 1.28 × 104, respectively. The multipole decomposition and near-field distributions show that these two QBICs are dominated by the electric quadrupole (EQ) and magnetic quadrupole (MQ). Furthermore, bidirectional optical switching can be accomplished by changing the polarization direction of the incident light. As a result, the maximum sensitivity and figure of merit (FOM) are 488.9 nm/RIU and 2.51 × 105 RIU-1, respectively. The results enrich our knowledge about BIC and reveal a platform for the development of high-performance photonics devices such as optical switches and sensors.

Multiple Fano Resonance Modes based Plasmonic Refractive Index Sensor for Edible Oil Adulteration Detection

Surface plasmon polariton (SPP)-based plasmonic sensors are increasingly replacing traditional bulky sensors in refractive index sensing, biosensing, food adulteration detection, and other applications due to their unique optical features and different Metal-Insulator-Metal (MIM) topologies. The present research introduces a new design for a highly sensitive MIM waveguide-based refractive index sensor. This design incorporates an innovative combination of an inverted U-shaped rectangular split-ring resonator (RSRR), a semi-circle-split-ring resonator (SCSRR), and a stub. The sensor’s wave-guiding capabilities, such as electromagnetic wave transmission, field profile distribution, and sensitivity, are meticulously analyzed using a two-dimensional finite-element method. The key objective of this device is to identify slight differences in the refractive index by observing shifts in resonant wavelength through the light’s interaction with the plasmonic structure. Moreover, optimizing the geometric parameters significantly enhances the sensor’s performance. The optimized sensor achieves a maximum refractive index sensitivity of 2400 nm/RIU, a figure of merit (FOM) of 45.28, and a Q-factor of 39.86, as demonstrated by simulation results. Further investigations reveal the MIM structure’s capacity to detect adulteration in edible oils, underscoring the sensor’s adaptability and its potential for widespread biosensing applications.

Fano resonances in dielectric metasurfaces with hemispherical voids: Effect on the optical Kerr nonlinearity

The optical behavior of the square lattices of the hemispherical nanovoids on the surface of the high-refractive-index all-dielectric slabs in the visible range is studied numerically using gallium phosphide as an example. There exist Fano resonances for these metasurfaces for a limited range of thicknesses. The Fano resonances are caused by the interference between the Mie-type scattering resonances of surface pattern elements and the Fabry–Pérot modes of the slabs. The maximum enhancements of the optical Kerr nonlinearity with respect to the bulk material are revealed at the Fano resonances, in particular, for the thinnest nanostructures. Interestingly, no positive correlation between the quality factor and the enhancement of the optical Kerr effect of the metasurface at the Fano resonances is observed.

Enhanced detection limit in an exceptional surface-based fiber resonator by manipulating Fano interference.

An exceptional surface (ES) has advantages in improving sensing robustness and enhancing frequency splitting. Typically, the eigenvalue splitting must exceed the mode linewidth in order to be clearly visible in the spectrum, which limits the precision of the ES-based sensing structure. In this paper, a strategy for manipulating spectral line shape in an ES-based structure is experimentally realized. In addition, the limit of the minimum detectable displacement can be further reduced by monitoring the peak intensity of the Fano interference line shape. The demonstration of Fano interference in an ES-based system opens the way for a new class of ultrasensitive optical sensors.

Modular Assembly of Metamaterials Using Light Gradients.

This is a report on a pilot study that tests the feasibility of assembling photonic metamaterials (PMs) using light gradient forces. Following a strategy that works like modular construction, light gradient forces, produced by a tightly focused, 1D standing wave optical trap, time-multiplexed across a 2D lattice are used to assemble voxels consisting of prefabricated, monodispersed nanoparticles (NPs) with radii ranging from 30 to 500nm into 3D structures on a hydrogel scaffold. Hundreds of NPs can be manipulated concurrently into a complex heterogeneous voxel this way, and then the process can be repeated by stitching together voxels to form a metamaterial of any size, shape, and constituency although imperfectly. Imperfections introduce random phase shifts and amplitude variations that can have an adverse effect on the band structure. Regardless, PMs are created this way using two different dielectric NPs, polystyrene and rutile, and then the near-infrared performance for each is analyzed with angle-, wavelength-, and polarization-dependent reflection spectroscopy. The cross-polarized spectra show evidence of a resonance peak. Interestingly, whereas the line shape from the polystyrene array is symmetric, the rutile array is not, which may be indicative of Fano resonance. So, even with the structural defects, reflection spectroscopy reveals a resonance.

Double tunable Fano resonance based on a metal–insulator–metal waveguide with double coupled cavities and its application

A metal–insulator–metal (MIM) waveguide with a ring cavity (RC) and a half ring cavity (HRC) is proposed to realize the detection of two mediums simultaneously based on independently tunable double Fano resonances. Utilizing numerical simulation of the finite element method, the transmission characteristics and magnetic field distribution are investigated. The simulation findings indicate that the structure is capable of generating double Fano resonances, and the two Fano resonances are tuning independently. The maximum sensitivity and figure of merit (FOM) are 2385 nm/RIU (refractive index unit) and 31886RIU−1, respectively, and these values are achieved by changing the structural parameters and the refractive index of the insulator. Moreover, the sugar content in flavor and the concentration of ethanol solution can be detected at the same time, which indicates the high efficiency of the sensor. Therefore, these performances demonstrate that the tunable double Fano resonance based on a MIM waveguide is a hopeful method for chemical detection.

Fano resonances in tilted Weyl semimetals in an oscillating quantum well

Considering the low-energy model of tilted Weyl semimetal, we study the electronic transmission through a periodically driven quantum well, oriented in the transverse direction with respect to the tilt. We adopt the formalism of Floquet scattering theory and investigate the emergence of Fano resonances as an outcome of matching between the Floquet sidebands and quasi-bound states. The Fano resonance energy changes linearly with the tilt strength suggesting the fact that tilt-mediated part of quasi-bound states energies depends on the above factor. Given a value of momentum parallel (perpendicular) to the tilt, we find that the energy gap between two Fano resonances, appearing for two adjacent values of transverse (collinear) momentum with respect to the tilt direction, is insensitive (sensitive) to the change in the tilt strength. Such a coupled (decoupled) behavior of tilt strength and the collinear (transverse) momentum can be understood from the tilt-mediated and normal parts of the quasi-bound state energies inside the potential well. We vary the other tilt parameters and chirality of the Weyl points to conclusively verify the exact form of the tilt-mediated part of the quasi-bound state energy that is the same as the tilt term in the static dispersion. The tilt orientation can significantly alter the transport in terms of evolution of Fano resoance energy with tilt momentum. We analytically find the explicit form of the bound state energy that further supports all our numerical findings. Our work paves the way to probe the tilt-mediated part of quasi-bound state energy to understand the complex interplay between the tilt and Fano resonance.

Enhanced cation ordering, electron-spin-phonon interactions and Fano resonance in half-metallic Sr2FeMoO6 thin films

We report the presence of electron-spin-phonon interactions in half-metallic ferromagnetic Sr2FeMoO6 (SFMO) double perovskite thin films using temperature-dependent Raman spectroscopy. A series of SFMO thin films have been prepared on LaAlO3 (001) single-crystal substrate using the Pulsed Laser Deposition technique. These depositions have been made in different gas-conditions such as in vacuum, and under nitrogen and oxygen gas pressures. At room temperature, Raman spectra manifest a Fano feature which indicates the presence of electron-phonon coupling in the films. The electron-phonon coupling strength further changes with a change in deposition conditions. Magnetization results show that the SFMO film grown in vacuum has the highest saturation magnetization which suggests better cation ordering as compared to the other films. For enhanced understanding, Raman spectra were recorded at varied temperatures and the data were analyzed by theoretical model fittings. A parameter quantifying temperature-dependent anharmonic nature of phonons has been derived using Balkanski model fits. This parameter shows a drastic deviation in the vicinity of Curie temperatures, manifesting a spin-phonon coupling in SFMO films. We further show that the spin-phonon coupling strengthens with improved Fe–Mo ordering. Any experimental observation of spin-phonon coupling has not been reported for SFMO systems till date. The magnetization data corroborate well with these observations made by Raman measurements. Our results of Raman spectroscopy, magnetization and resistivity collectively suggest that the SFMO films exhibit electron-spin-phonon interactions, which are influenced by the cation ordering. We also devised out the method of relating the anharmonic nature of Raman modes with the degree of Fe–Mo ordering and spin-phonon coupling in double-perovskite materials.

Optical terahertz metamaterial switch controlled via high-stability CsPbBr3 microcrystals

Dynamic control of terahertz metamaterials using thin organic perovskite active layers has been extensively researched. However, the preparation of organic perovskite devices requires strict environmental conditions, and the devices are prone to hydrolysis in air, which reduces performance. Herein, we report an optical terahertz metamaterial switch controlled via hybridization with high-stability CsPbBr3 microcrystals prepared through precipitation from a water–dimethylformamide (DMF) mixed-solution. Under light excitation, a modulation factor of 24% was achieved based on the photoelectric and photothermal effects of the CsPbBr3 microcrystals. After exposure to air for four months, the modulation factor remained essentially unchanged, demonstrating the exceptional stability of the system generated. Following the integration of CsPbBr3 microcrystals with the metamaterial, a frequency-shift of its dipole resonance and switching of Fano resonance was achieved, providing a novel approach to dynamic control of terahertz waves.

Dynamically Tunable Half‐Ring Fano Resonator Based on Black Phosphorus

A tunable material black phosphorus (BP) terahertz (THz) half‐ring Fano resonator is proposed, exhibiting enhanced sensitivity, tunable frequency parameters, and the flexible sensing range. A half‐ring is positioned above the main channel, while a groove is excavated beneath it to produce the Fano resonance. The discrete mode of the half‐ring is coupled with the continuous mode of the groove, leading to a significantly enhanced sensitivity. This sensor can pick up subtle changes in the surrounding environment. Additionally, the incorporation of BP into the half‐ring positioned above the channel enables the flexible adjustment of the Fano resonator's resonant frequency. This adjustment is achieved through the manipulation of the electron doping concentration of the BP material. At the third‐order resonance around 5.81 THz, the frequency shift margin can reach 160 GHz. Adjusting the structural parameters of the Fano resonator, such as the radius of its outer ring, the distance of this ring to the main channel, and the groove's height, significantly affects its transmission spectrum. The Fano resonator demonstrates its considerable potential for applications in the field of integrated electronics. It not only provides an innovative design perspective, but also lays the foundation for the study of THz systems.

Combined acoustic metamaterial design based on multi-channel Fano resonance effect

In response to the increasing traffic noise problem, we designed a combined acoustic metamaterial (CAM) based on the multi-channel Fano resonance principle. By utilizing the Fano resonance coupling between the acoustic spiral structure and the hollow structure, efficient sound insulation under effective ventilation conditions is achieved. Simulation results of acoustic transmission loss show that the acoustic transmission loss of CAM is more than 13 dB in the frequency band of 520–989 Hz. The broadband sound insulation characteristic can block the oblique angle incident sound waves from different angles. Simulation results of the elastic strain energy and acoustic pressure field validate the sound insulation mechanism of the Fano resonance of the combined acoustic metamaterial. The experimental results in the impedance tube generally agree with the simulation results. To explore the possibility of wider engineering applications of CAM, we propose a combined CAM and CAM0.7 structure. The results show that a series structure of acoustic metamaterials can be selected to further realize broadband sound insulation within 500–1574 Hz.

Frequency‐Space Selective Fano Resonance Based on a Micro‐Ring Resonator on Lithium Niobate on Insulator

AbstractCorresponding to the different phase‐shifts of the interference modes, the whispering gallery mode resonator‐based Fano resonance exhibits a variety of unique spectral lineshapes that can be applied to sensing, optical signal processing, and so on. However, most approaches to lineshape tuning aim to alter the propagation phase‐shift or coupling strength, and generally suffer from relatively low efficiency and limited tuning range. In this paper, with a carefully designed waveguide‐taper coupled micro‐ring resonator structure and the assistance with the grating‐coupler, for the first time a near full‐lineshape selectivity of the Fano resonance is demonstrated in two isolated tuning dimensions of the frequency and transverse space, which means arbitrary lineshapes including the Lorentzian‐dip, asymmetric Fano peak or electromagnetically‐induced‐transparency (EIT)‐like peak can be obtained at a specific resonance wavelength in the whole C‐band. In addition to the different types of line shapes, the extinction ratio can also be enhanced by dynamically tuning the coupling position. This research provides an efficient approach to manipulate the transmission spectra of the Fano resonance, which is of great importance in promoting its further applications on integrated photonics platforms.

High-Q magnetic toroidal dipole resonance in all-dielectric metasurfaces

High quality (Q) factor toroidal dipole (TD) resonances have played an increasingly important role in enhancing light–matter interactions. Interestingly, TDs share a similar far-field distribution as the conventional electric/magnetic dipoles but have distinct near-field profiles from them. While most reported works focused on the electric TD, magnetic TDs (MTDs), particularly high-Q MTD, have not been fully explored yet. Here, we successfully realized a high-Q MTD by effectively harnessing the ultrahigh Q-factor guided mode resonances supported in an all-dielectric metasurface, that is, changing the interspacing between silicon nanobar dimers. Other salient properties include the stable resonance wavelength but a precisely tailored Q-factor by interspacing distance. A multipole decomposition analysis indicates that this mode is dominated by the MTD, where the electric fields are mainly confined within the dielectric nanostructures, while the induced magnetic dipole loops are connected head-to-tail. Finally, we experimentally demonstrated such high-Q MTD resonance by fabricating a series of silicon metasurfaces and measuring their transmission spectra. The MTD resonance is characterized by a sharp Fano resonance in the transmission spectrum. The maximum measured Q-factor is up to 5079. Our results provide useful guidance for realizing high-Q MTD and may find exciting applications in boosting light–matter interactions.

Phenomenology of Intermediate Molecular Dynamics at Metal-Oxide Interfaces.

Reaction intermediates buried within a solid-liquid interface are difficult targets for physiochemical measurements. They are inherently molecular and locally dynamic, while their surroundings are extended by a periodic lattice on one side and the solvent dielectric on the other. Challenges compound on a metal-oxide surface of varied sites and especially so at its aqueous interface of many prominent reactions. Recently, phenomenological theory coupled with optical spectroscopy has become a more prominent tool for isolating the intermediates and their molecular dynamics. The following article reviews three examples of the SrTiO3-aqueous interface subject to the oxygen evolution from water: reaction-dependent component analyses of time-resolved intermediates, a Fano resonance of a mode at the metal-oxide-water interface, and reaction isotherms of metastable intermediates. The phenomenology uses parameters to encase what is unknown at a microscopic level to then circumscribe the clear and macroscopically tuned trends seen in the spectroscopic data.

Multiple Fano Resonances Enabled by the Interference between an Out‐of‐Plane Plasmon Mode and Fabry–Pérot Cavity Modes

AbstractMultiple Fano resonances (mFRs) are arising as a promising optical platform to achieve precise sensing and detection. However, experimentally achieving mFRs by simple structures has remained challenging, which impedes the widespread applications of mFRs. Herein a simple structure composed of a single colloidal metal nanoparticle and a transition metal dichalcogenide flake to simultaneously achieve up to 8 FRs in experiments is demonstrated. Combining theoretical and experimental techniques, that an out‐of‐plane plasmon mode of the metal nanoparticle interferes with the Fabry–Pérot cavity modes from the WS2 flake to form mFRs in the visible region is proved. The simplicity and generality of the method further allow us to systematically study the tunability of the mFRs, in terms of the peak/dip positions and the number of FRs, by changing the structural parameters, which include the thickness of the WS2 flake, size and shape of the plasmonic nanoparticle. In addition, the quality of the mFRs is proved to be adjustable by tuning the reflectivity of the substrate in the system. The highest quality factor and spectral contrast of the achieved resonances are up to ≈180 and ≈0.95, respectively. The simple structure and high‐quality optical modes will prosper applications in precise sensing and light modulation.

Stretchable Metamaterials with Tamm/Fano Resonances for Tunable, Efficient Mechanochromic Color Shifting

AbstractNext‐generation wearable and optoelectronic technologies requires highly adaptable light manipulation capabilities for applications in sensors, displays, and optical switches on flexible substrates. Here, a cost‐effective approach is presented for realizing a Tamm Plasmon (TP) resonant device on a flexible platform by combining nanoimprint lithography with layer‐by‐layer assembly. The TP device incorporates a stretchable, 1D bragg (BRG) stack coupled with a gold (Au) and aluminum (Al) metasurface, whose dimensions are designed to enable tunability in the visible and near‐infrared (NIR) regions of the spectrum. The device exhibits substantial reflected intensities (≈75%) and a well‐defined, narrow TP minimum of approximately 30 nm. Both TP and Fano resonances can be clearly observed by incorporating symmetry‐broken metasurface features with the BRG stack. The integrated system is subjected to both uniaxial (up to 37% strain) and biaxial (up to 25% strain) stretching, demonstrating dynamic chromatic responses in both the visible and near‐infrared regimes with sensitivities of ≈6.2 nm/%. This work clearly demonstrates a cost‐effective route for the fabrication of multi‐plasmon resonant devices with tunable colors on a flexible platform.